Referring to FIG. 1, a conventional voltage converting device for a light emitting device (e.g., an LED device) includes a frontend boost-type AC-DC converter 4 with power factor correction, and a backend half-bridge LLC resonant DC-DC converter 5. Since each of the frontend stage and the backend stage of such a conventional voltage converting device requires a dedicated controller, the entire voltage converting device may include at least three power switches, which results in relatively high circuit complexity due to the number of circuit components, resulting in high costs.